Microelectronic devices, such as semiconductor devices and field emission displays, are fabricated on and/or in microelectronic workpieces using several different apparatus (“tools”). Many such processing apparatus have a single processing station that performs one or more procedures on the workpieces. Other processing apparatus have a plurality of processing stations that perform a series of different procedures on individual workpieces or batches of workpieces. The workpieces are generally handled within the processing apparatus by automatic handling equipment (i.e., robots) because microelectronic fabrication requires extremely clean environments, very precise positioning of the workpieces, and conditions that are not suitable for human access (e.g., vacuum environments, high temperatures, chemicals, etc.).
An increasingly important category of processing apparatus are plating tools that plate metals and other materials onto workpieces. Existing plating tools use automatic handling equipment to handle the workpieces because the position, movement and cleanliness of the workpieces are important parameters for accurately plating materials onto the workpieces. The plating tools can be used to plate metals and other materials (e.g., ceramics or polymers) in the formation of contacts, interconnects and other components of microelectronic devices. For example, copper plating tools are used to form copper contacts and interconnects on semiconductor wafers, field emission displays, read/write heads and other types of microelectronic workpieces. A typical copper plating process involves depositing a copper seed layer onto the surface of the workpiece using chemical vapor deposition (CVD), physical vapor deposition (PVD), electroless plating processes, or other suitable methods. After forming the seed layer, copper is plated onto the workpiece by applying an appropriate electrical field between the seed layer and an anode in the presence of an electrochemical plating solution. The workpiece is then cleaned, etched and/or annealed in subsequent procedures before transferring the workpiece to another apparatus.
Single-wafer plating tools generally have a load/unload station, a number of plating chambers, a number of cleaning chambers, and a transfer mechanism for moving the microelectronic workpieces between the various chambers and the load/unload station. The transfer mechanism can be a rotary system having one or more robots that rotate about a fixed location in the plating tool. One existing rotary transfer mechanism is shown in U.S. Pat. No. 6,136,163 issued to Cheung, et al., which is herein incorporated by reference in its entirety. Alternate transfer mechanisms include linear systems that have an elongated track and a plurality of individual robots that can move independently along the track. Each of the robots on a linear track can also include independently operable end-effectors. Existing linear track systems are shown in U.S. Pat. No. 5,571,325 issued to Ueyama, et al., PCT Publication No. WO 00/02808, and U.S. patent application Ser. Nos. 09/386,566; 09/386,590; 09/386,568; and 09/759,998, all of which are herein incorporated in their entirety by reference. Many rotary and linear transfer mechanisms have a plurality of individual robots that can each independently access most, if not all, of the processing stations within an individual tool to increase the flexibility and throughput of the plating tool.
These robots use end-effectors to grasp the workpiece in moving the workpiece from one processing station to another. The nature and design of the end-effectors will depend, in part, on the nature of the workpiece being handled. In some circumstances, the backside of the workpiece is not overly sensitive and may be contacted by the end-effector. In such circumstances, a vacuum-based end-effector may be used. Such vacuum-based end-effectors typically have a vacuum plenum having a plurality of vacuum outlets.
Some workpieces are not tolerant of such contact, though. Such workpieces typically must be handled by their edges and the distance inwardly from the edge of a workpiece which handling equipment may contact is strictly proscribed. This significantly limits the area of contact between the end-effectors and the workpieces, making it more difficult to securely grasp the workpiece during handling. If the workpiece is not grasped adequately, it may slide off the end-effector during movement of the robot in transferring the workpiece from one processing station to another. This problem is particularly acute where the end-effector is rotated to flip the workpiece from one horizontal orientation to an inverse horizontal orientation, e.g., to properly position a semiconductor wafer in an electroplating chamber.
It would be advantageous to confirm that a workpiece is properly positioned on and grasped by an end-effector before the end-effector moves the workpiece. International Publication No. WO 00/02808, which is incorporated herein in its entirety by reference, suggests using light reflected off the workpiece to determine the presence of a workpiece. A lack of reflected light indicates that no workpiece is present. While such a system does indicate whether a workpiece is in the proper vicinity, it does not ensure that the end-effector has properly grasped the workpiece.
Most current end-effectors use three spaced-apart points of contact with the workpiece to define a plane within which the workpiece will be received. Such three-point contact is able to adapt to minor dimensional differences from one workpiece to the next. Grasping the edge of the workpiece at four locations can lead to a more secure grip of a workpiece which is precisely the anticipated size. If the workpiece falls outside of very narrowly proscribed tolerances, however, it is difficult to ensure that all four contact points are gripping the edge of the workpiece with sufficient force to securely hold the workpiece to the end-effector.